Semiconductor devices have become widespread in use in modern society, and indeed, have become indispensable in a variety of devices and services. Nevertheless, these devices are still prepared from a basic silicon wafer substrate that is treated by a variety of processes that selectively etch, and deposit films to produce microscopic structures in the wafer to allow it to perform its desired functions in electronic applications.
In the manufacture of semiconductor devices from silicon wafers, it is sometimes desirable to create a high aspect ratio contact hole in interlayer dielectrics which is filled with tungsten. However, it is for many reasons considered undesirable to permit direct contact between the tungsten plug and the dielectric layer. As a result, a "barrier layer" or "barrier film" is usually employed to separate the tungsten plug from the dielectric layer. However, present methods for forming such a barrier layer are inadequate, and lead to "plug loss" and a defective device. As shown in FIG. 1A, depicting the prior art, when a high aspect ratio hole 10' in a dielectric layer is coated with titanium nitride (TiN) film 12' using physical vapor deposition (PVD) as is conventional, the PVD TiN coating does not conform to the hole, i.e. it does not cover the entire surface of the high aspect ratio hole. Rather, the lower extremities 14' of the hole are not covered, while the base 16' and upper extremities 18' are covered. If this hole were filled with tungsten, there would be direct contact with the dielectric layer S As a result, conventional techniques for forming a barrier layer instead rely on using the chemical vapor deposition (CVD) process. As shown in FIG. 1B, the CVD process forms a conformal layer 20' in the high aspect hole 10'. The hole can then be filled with tungsten (W) to form plug 22', for example by chemical vapor deposition or another technique. Thereafter, however, dry etching of the tungsten layer inevitably results in "plug loss"the upper portion of the plug is removed during the etching process, as shown in FIG. 1C, resulting in a defective device.
There yet exists a need for a method of forming a tungsten plug during semiconductor device fabrication, that maintains substantially the entire plug and reduces plug loss to insignificance. Preferably, the method should be relatively inexpensive and simple to integrate into standard semiconductor fabrication techniques.